There are many electronic scales on the market which weigh articles, such as letters, packages, and other postal articles, and perform a computation such as the exact United States Postal Service or United Parcel Service charges, including various ways of converting zip code numbers to zone numbers for entering into a computer for making the computation. However, they are all very expensive machines which are generally uneconomical or not affordable by the small office or home having relatively small or (under about 50) daily usage requirements. In general, it may be said that these electronic weighing systems are too complex and expensive for the average small user.
The object of the present invention is to provide a low cost and accurate electronic weighing system. A further object of the invention is to provide an electronic weight transducer which is relatively rugged. A further object of the invention is to provide such an electronic weighing system which is easily assembled from relatively few components.
In accordance with the invention, the transducing of the weight of an article to an electrical analog signal is performed by means of a novel parallelogram linkage and cantilever beam-strain gauge assembly. The parallelogram linkage has a fixed or stationary link which is adapted to be nested in and secured to an injection molded housing frame and securely fastened. The cantilever sensing beam, having bonded strain gauges on the tension and compression sides or surfaces thereof, has the free end of the beam connected to the movable parallel link of the parallel linkage (which is opposite to the fixed or stationary link) by a flexible coupling member so that even though there may be sidewise play in the linkage, the vertical component of force applied to the free end of the cantilever beam is an accurate measure of the vertical force thereon. The scale pan is secured to the movable parallel link so that any article resting on the pan transmits a force to the link which is thereby converted to an electrical signal by the strain gauges. The strain gauges are connected in an electrical bridge circuit to provide, at very low cost, an accurate electrical analog signal and an analog to digital converter preferrably controlled by a microprocessor, produces digital signals for display and computation purposes. The analog to digital converter is controlled by the microprocessor which also controls a keyboard and display functions input.